Using the National Center for Education Statistics 2002-2012 Educational Longitudinal Study (ELS) data set, this study examines the relation between college undermatching and bachelor's degree attainment, and whether the influences of undermatching on bachelor's degree attainment vary by race/ethnicity. Results revealed students who undermatched were less likely to graduate college within 4 years, as well as 6 years, than students who matched to a college commensurate with their academic qualifications. The evidence also showed the negative relation between college completion and undermatching was stronger among students with a relatively high probability of graduation. Thus, policymakers and educators need to be concerned about bachelor's degree attainment for even highly qualified students if they are undermatched. Our results also illustrate that race/ethnicity and undermatching effects on degree completion can be best understood in concert rather than separately. It suggests that undermatching can be a mechanism for structural inequality in terms of bachelor's degree attainment across racial/ethnic groups. In particular, the bachelor's degree attainment gap among Hispanics based on undermatching was the largest across race/ethnicity groups. We highlight the importance of addressing Hispanic undermatching, as Hispanics show the greatest negative effects of undermatching among all student groups.